Birger Kristian Eriksen (17 November 1875 – 16 July 1958) was a Norwegian officer (with the rank of Oberst) who was instrumental in stopping the first wave of Gruppe 5 of the German invasion force outside Oslo. Eriksen was the commander of Oscarsborg Fortress when Nazi Germany attacked Norway in the early hours of 9 April 1940. He gained lasting recognition for ordering the fortress under his command to open fire on the vanguard forces of Operation Weserübung and sinking the 14,000 ton heavy cruiser Blücher.